Production of Lactic Acid by Fermentation
Lactic acid can be produced by the continuous or batch fermentation of sugars or other biomass streams such as hydrolized starch, sulfite waste liquor or cheese whey.
For a rapid and economic fermentation, the pH of the broth is usually maintained in the range of 5.2-6.8 by either (a) continuously removing lactic acid such as by extraction, or membranes, or ion exchange, or electrodialysis, or (b) continuously adding a base such as aqueous ammonia, calcium carbonate, calcium hydroxide, or sodium hydroxide, or (c) starting the fermentation with a growth medium with substantial buffering capacity, such as a calcium carbonate slurry.
In each case, the fermentation broth may or may not have the fermentation microorganisms or enzyme slurry removed.
FIG. 1 illustrates one method of preparing a concentrated fermentation broth. Steps (1) to (3) are not part of the present invention, but are included for illustrative purposes only. Fermentation takes place in unit 1 where nutrients and whey/permeate are fermented at about 40.degree. C., and a pH of about 5.6. The stream from the fermentation unit 1 containing about 10-12% lactate salt optionally is filtered by membrane filter or centrifuge 2, which removes the biomass and any other solids. The aqueous stream leaving the filter contains about 95 g/l of lactate salt and 2 g/l of succinate salt, 1 g/l of acetate salt and other impurities.
This stream from filter 2 goes to an evaporator 3, where excess water is removed to give a concentrated broth containing 10-40% water, the balance being primarily the lactate salt of the base used for fermentation pH control.